Caller ID. 1. the digital display on a phone that identifies the number
from which the call originates; 2. so cool; provides the all-important
function of identifying the boss's call, the annoying friend's call, the
potential employer's call, and offers the added bonus of acting as a pop
quiz on area codes nationwide.

I now know both of San Diego's area codes (858 and 619), and I was so
good at jumping up to take calls that I tipped my office-mate off to the
fact that something was up, proof that one can't actually win when it
comes to communication security. (Maybe if I put my phone on vibrate so
he couldn't actually hear it ringing...)